CP-51278: define import_activate datapath operation

This is to be used as part of the inbound storage migration process
and will make available a UNIX domain socket which can have an open
file descriptor passed to it via SCM_RIGHTS. This takes the place of
the /run/blktap-control/nbdserver<pid>.<minor> path used in SXM on
SMAPIv1.

Implementations shall arrange to make available a mechanism whereby an
open file descriptor can be passed and then used to connect to an
active new-fixed NBD server providing access to the specified [uri]

Signed-off-by: Mark <[email protected]>

ocaml/xapi-storage/generator/lib/data.ml

@@ -68,6 +68,14 @@ let domain =
     ~description:["An opaque string which represents the Xen domain."]
     domain
 
+(** Path to a UNIX domain socket *)
+type sock_path = string [@@deriving rpcty]
+
+let sock_path =
+  Param.mk ~name:"sock_path"
+    ~description:["A path to a UNIX domain socket in the filesystem."]
+    sock_path
+
 open Idl
 
 module Datapath (R : RPC) = struct
@@ -132,6 +140,23 @@ module Datapath (R : RPC) = struct
       ]
       (dbg @-> uri_p @-> domain @-> returning unit error)
 
+  let import_activate =
+    declare "import_activate"
+      [
+        "[import_activate uri domain] prepares a connection to the "
+      ; " storage named by [uri] for use by inbound import mirroring, "
+      ; "the [domain] parameter identifies which domain to connect to, "
+      ; "most likely 0 or a custom storage domain. The return value is a "
+      ; "path to a UNIX domain socket to which an open file descriptor "
+      ; "may be passed, by SCM_RIGHTS. This, in turn, will become "
+      ; "the server end of a Network Block Device (NBD) connection "
+      ; "using, new-fixed protocol. Implementations shall declare the "
+      ; "VDI_MIRROR_IN feature for this method to be supported. It is "
+      ; "expected that activate will have been previously called so that "
+      ; "there is an active datapath."
+      ]
+      (dbg @-> uri_p @-> domain @-> returning sock_path error)
+
   let deactivate =
     declare "deactivate"
       [